Gamma Ray Detectors

Germanium is very similar to Si, but its band gap is too small for many practical applications. Large crystals of ultra-high-purity Ge have been grown for use as gamma-ray detectors. In such crystals, the net concentration of... 

Electronic and Optoelectronic Applications of TeUurides. Most metal teUurides are semiconductors with a large range of energy gaps and can be used in a variety of electrical and optoelectronic devices. AUoys of the form HgCdTe and PbSnTe have been used as infrared detectors and CdTe has been employed as a gamma ray detector and is also a promising candidate material for a thin-fUm solar ceU. 

A. J. Strauss, Proceedings of the International Symposium on Cadmium Telluride as a Materialfor Gamma-ray Detectors, 1972, p. I-l. 

There is always some level of ambient radioactivity in an environment. This radiation is known as background radiation. Measure and record the background activity by recording the counts registered by the gamma ray detector in 30-s intervals for 5 min. Record the data in Data Table 1. 

External microbeam scans may be conducted in air, if analyses in vacuo are difficult to perform on a given specimen. The thin specimen is placed 100 pm from the exit foil of the microbeam, and the gamma-ray detector is placed just behind the sample. 

In almost every case, experimenters who use the resonant nuclear reactions have chosen to detect and count the gamma rays, but the alpha particles can also be used (Umezawa et al., 1987, 1988a). There seems to be no published comparison of the results using alpha particle and gamma ray detection. Fig 2 shows a typical experimental setup using a gamma ray detector. 

Gamma-ray counters Gamma ray detector Gamma-rays... 

Fig. 5.22. Experimental set-up for studies of positron impact inner shell ionization (Ebel et al, 1989). Key (1) target support (2) lead collimator (3) flange with thin window for the transmission of X-rays to (4) a Si(Li) detector (5) aluminium window 0.1 mm thick (6) Nal(Tl) gamma-ray detector.

Recently, the development of extremely high resolution solid state Ge(Li) gamma-ray detectors, the application of gamma-gamma coincidence techniques, and the availability of low cost 14 MeV neutron generators have renewed interest in activation analysis as a means for routine rapid and non-destructive elemental abundance determinations of both major and trace elements. Some of these new techniques will be discussed in the sections that follow. 

The recent general availability of solid state Ge(Li) gamma-ray detectors has made possible new applications of activation analysis to multielement trace analysis. A simplified schematic representation of a Ge(Li) detector is given in Fig. 6. The principal advantage of these detectors is their excellent energy resolution for gamma-ray spectrometry 52>. While a typical 3 X 3" NaI(Tl) scintillation crystal may have a photopeak resolution of 50 KeV fwhm (/ull width at Aalf maximum) for the 137Cs... 

Some coal analyzers use several gamma-ray detectors and operate by the use of neutron pulses. Such analyzers can measure the density and sulfur content of coal along with its heating value, moisture, and volatile matter content. This pulsed fast/thermal neutron analyzer can be self-calibrating and can determine such elements as carbon, oxygen, and sodium. 

It is also interesting to note that the limitations of most neutron systems lie not in the neutron source(s) but rather in the (gamma ray) detectors and subsequent data acquisition system. The obvious need is for development of detectors with higher rate capability and improved energy resolution. All modern digital data processing techniques have allowed significant improvement in the performance of conventional scintillation detectors with respect to rate and pileup rejection. 

Alpha-particle detector Beta-particle detector Gamma-ray detector proportional counters silicon (Si) diode with spectrometer proportional counters Geiger-Muller counters liquid scintillation (LS) counters thallium-activated sodium iodide (Nal(Tl) detector with spectrometer germanium (Ge) detector with spectrometer... 

Carefully swirl to mix. Be certain to cover the bottom evenly, but do not swirl the solution up onto the container walls. The total initial volume is 5.0 mL. Screw the lid on the container and carefully place in position in the germanium gamma-ray detector counting chamber it should be centered and level. Count twice for a sufficient time period to accumulate 2000 counts (typically 100 s). Check to confirm that at least 2,000 counts have been accumulated at each of the peaks used for calibration. Collect the gross gamma-ray count rates for the full-energy peaks in Data Table 2B.1. 

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